The long term goals of our research are to understand how metabolic stress perturbs cellular homeostasis and to identify drugs that restore homeostasis by ameliorating this stress. The molecular pathogenesis of oligodendrocyte disorders, from rare diseases like Pelizaeus-Merzbacher disease (PMD) to common diseases like multiple sclerosis, involves a metabolic stress pathway known as the unfolded protein response (UPR). We will study oligodendrocytes as the model cell and use naturally-occurring missense mutations in the proteolipid protein (Plp1) gene to induce the UPR in vivo (i.e. mouse models) and in vitro (transfected cells). To gain insights into this metabolic stress, we will manipulate UPR signaling to alter the pathophysiology associated with mutant Plp1 expression. To do this, we will examine the function of the decoy kinase, Trb3, which is the central regulator of the UPR and Akt signaling pathways. Our work indicates that these pathways are involved in the pathogenesis of PMD and that overexpressing Trb3 in oligodendrocytes ameliorates the clinical phenotype of rsh mice. Our overall hypothesis is that Trb3 functions in UPR signaling to reduce the negative effects of metabolic stress on oligodendrocytes. In Specific Aim#1, the level of Trb3 overexpression in rsh oligodendrocytes that is necessary to ameliorate the phenotype will be determined. We have generated six transgenic lines expressing Trb3 at different levels and find that the highest expressor reduces the rsh phenotype and virtually eliminates UPR activation by three months of age. In the absence of Trb3 overexpression, the UPR remains unabated at this age. We will use electrophysiology, behavior, ultrastructure and expression analyses to determine a dose-response curve for Trb3 function as well as a timeline for disease amelioration. In Specific Aim#2, we will explore the interaction of Trb3 with the ATF4 protein in the UPR as well as Akt signaling. Published studies indicate that Trb3 interacts with ATF4 and Akt. Our data shows that deleting the Akt1 gene in oligodendrocytes reduces the rsh phenotype. And we will determine if deleting Atf4 in oligodendrocytes also reduces the rsh phenotype.